| Before 1920 he had shown that the homology of a simplicial complex is a topological invariant. |
| They both fail for open set logic, which is to say intuitionism, just as they both fail for its topological dual, closed set logic. |
| However he continued to work on topological ideas, in particular embedding complexes in Euclidean space. |
| He combined topological and metrical methods to attack problems of real analysis. |
| He seems to be just as good at bringing mathematics to life, especially rather elaborate topological constructions. |
| He worked, in particular, on the theory of topological and metric mappings on 2-dimensional space. |
